The invention relates to an automatic sampling device or auto-sampler to be used in a gas chromatograph or the like, in particular a syringe mechanism suitable for automatically sampling a gas.
In a gas chromatography, a syringe is often used for introducing an analyzing sample into a gas chromatograph. In this method, at first, a predetermined amount of a sample is sacked from a sample container capped with, for example, a rubber septum by means of a syringe. Then, a needle of the syringe is inserted into a rubber septum covering a sample pouring opening of the gas chromatograph, and the sucked sample is pored into the pouring opening.
However, there have been several problems in using the conventional syringe.
First, since an opening of a hollow needle of the syringe is open, especially after a gas is taken therein, during a period from a time when the gas is taken by the syringe to a time when the gas is poured or supplied into the pouring opening of the gas chromatograph, the gas may leak out of the opening of the needle due to diffusion, or on the contrary, air may enter therein to thereby decrease an accuracy of the sampling.
As a countermeasure for the problem, a syringe valve to be mounted between a barrel and the needle of the syringe has been developed. However, in case the syringe valve is used, a dead space is increased, or the sample or air entering into a minute portion of the valve may interrupt the next sampling. In other words, contamination is liable to take place. Also, as a simple solution, there has been developed a needle cap formed of a small soft plastic member for covering a tip of the needle. However, in this case, a troublesome labor for attaching or detaching the needle cap is required whenever a sampling is carried out.
Further, there is a serious problem that both the syringe valve and needle cap can not be applied to the automatic sampling device. More specifically, it is difficult to automatically open or close the valve mounted on a part of the syringe, or automatically attach or detach the cap to or from the tip of the needle by a machine. Even if the syringe valve and needle cap could be applied to the automatic sampling device by some complicated mechanism, reliability of the movement would not be expected. Thus, applications of the valve and cap to the automatic sampling device are practically impossible.
A second problem in sampling by the syringe is a bending or breaking of a needle. In case the needle of the syringe is inserted into the septum covering the pouring opening of the gas chromatograph, since the septum is generally very hard, and a septum made of a special material wherein a heat resisting property is increased to suppress a bleeding is especially very hard, a large force has to be applied to the needle linearly in the axial direction of the syringe. If a force slightly deviated from the axis direction is applied, there is a risk of bending the needle. Especially, an unexperienced user is liable to fail to thereby bend the needle.
Accordingly, an object of the invention is to provide an automatic sampling device, wherein in case a gas sampling operation is carried out, leakage of the gas from an opening of a needle due to diffusion of the gas can be prevented.
Another object of the invention is to provide an automatic sampling device as stated above, wherein bending of the needle can be prevented when the needle is inserted into a septum covering a pouring opening of a sample bottle.
Further objects and advantages of the invention will be apparent from the following description of the invention.